1. Field of the Invention
The present invention relates to an image processing apparatus which detects a character, in particular, large dots, in image data and performs a suitable image processing for the detected image, an image reading apparatus equipped with the image processing apparatus, an image forming apparatus equipped with the image processing apparatus, and a color copier equipped with the image processing apparatus.
2. Description of the Related Art
For example, Japanese Patent No. 2778669 discloses an image processing method that uses the technology of the type as mentioned above. In this image processing method, when detecting a dot in image data, the computation of a peak pixel is performed for the pixels of the image data which are located at predetermined positions.
Moreover, Japanese Laid-Open Patent Application No. 8-149294 discloses an image processing method that is known and is of the above type. In this image processing method, the computation of a peak pixel is performed for the pixels of the image data which are located at predetermined positions by using a plurality of matrices. Japanese Laid-Open Patent Applications No. 8-149289, No. 8-204968 and No. 8-149291 disclose image processing methods that are also known and of the above type. In these image processing methods, the determination of a dot in image data is performed by detecting the periodicity. Furthermore, Japanese Laid-Open Patent Application No. 9-51432 discloses an image processing method which is known and is of the above type. In this image processing method, the determination of a dot is made when a predetermined periodicity difference is small.
However, in each of the above-mentioned conventional methods, when detecting a low-linear-density dot (100 or less lines), the difference between the low-linear-density dot and a small character in the image data becomes very small. It is difficult that each of the conventional methods performs the segmentation of a small character and a dot. Each of the conventional methods does not take into consideration for the segmentation of a small character and a dot in image data when detecting a low-linear-density dot.
An object of the present invention is to provide an improved image processing apparatus in which the above-described problems are eliminated.
Another object of the present invention is to provide an image processing apparatus that can easily and correctly perform the segmentation of a small character and a dot even when the linear density is low.
Another object of the present invention is to provide an image processing apparatus that segments image data into a low-linear-density dot region and a normal dot region and performs selectively one of a first image processing for the low-linear-density dot region and a second image processing for the normal dot region, so that it can create good picture quality.
Another object of the present invention is to provide an image forming apparatus that outputs the processed image with good picture quality by using an image processing apparatus that easily and correctly performs the segmentation of a small character and a dot.
The above-mentioned objects of the present invention are achieved by an image processing apparatus that processes image data and outputs the processed image data, the image processing apparatus comprising: a maximum/minimum density detecting unit detecting whether a center pixel of a matrix of Nxc3x97N pixels in the image data has a maximum or minimum density among the pixels of the matrix; a center pixel selecting unit selecting one of neighboring pixels of the matrix adjacent to the center pixel as being an active center pixel; a diagonal pixel selecting unit selecting one of pairs of diagonal pixels of the matrix at positions symmetrical with respect to the center pixel as being active diagonal pixels; a determination unit determining whether the absolute value of a difference between an average of densities of all the pairs of diagonal pixels selected by the diagonal pixel selecting unit and a density of the center pixel selected by the center pixel selecting unit is larger than a predetermined threshold value; a peak pixel detecting unit detecting peak pixels of the matrix, each peak pixel being the center pixel detected as having the maximum or minimum density by the maximum/minimum density detecting unit, and the absolute value of the difference with respect to the center pixel determined as being larger than the threshold value by the determination unit; and a dot region detecting unit detecting one of the neighboring pixels including the peak pixels as being a dot region based on a relationship between the number of the peak pixels in a two-dimensional target region and the number of the peak pixels in each of two-dimensional neighboring regions of the target region.
The above-mentioned objects of the present invention are achieved by an image processing apparatus that includes a low-linear-density dot region detection device and an image processing device, the image processing device processing image data and outputting the processed image data, the low-linear-density dot region detection device comprising: a maximum/minimum density detection unit detecting whether a center pixel of a matrix of Nxc3x97N pixels in the image data has a maximum or minimum density among the pixels of the matrix; a determination unit determining whether the absolute value of a difference between an average of respective densities of all pairs of diagonal pixels of the matrix at positions symmetrical with respect to the center pixel and a density of the center pixel is larger than a predetermined threshold value; a peak pixel detection unit detecting peak pixels of the matrix, each peak pixel being the center pixel detected as having the maximum or minimum density, and the absolute value of the difference with respect to the center pixel determined as being larger than the threshold value; a peak pixel erasing unit making the detected peak pixels inactive when a periodicity between the detected peak pixels is below a fixed value; and a low-linear-density dot region detecting unit detecting one of neighboring pixels of the matrix, including a target center pixel, as being a low-linear-density dot region based on a relationship between the number of the peak pixels in a two-dimensional target region and the number of the peak pixels in each of two-dimensional neighboring regions of the target region, wherein the image processing device performs selectively one of a first image processing for pixels of the low-linear-density dot region detected by the low-linear-density dot region detection device and a second image processing for pixels of another dot region of the image data.
The above-mentioned objects of the present invention are achieved by a color copier that includes an image processing apparatus, an image reading device and an image printing device, the image reading device reading an image data from a document by color separation and supplying the image data to the image processing apparatus, and the image printing device forming a reconstructed image based on a processed image data output by the image processing apparatus and printing the reconstructed image, the image processing apparatus comprising: a maximum/minimum density detecting unit detecting a center pixel of a matrix of Nxc3x97N pixels in the image data that has a maximum or minimum density among the pixels of the matrix; a center pixel selecting unit selecting one of neighboring pixels of the matrix adjacent to the center pixel as being an active center pixel; a diagonal pixel selecting unit selecting one of pairs of diagonal pixels of the matrix at positions symmetrical with respect to the center pixel as being active diagonal pixels, a determination unit determining whether the absolute value of a difference between an average of densities of all the pairs of diagonal pixels selected by the diagonal pixel selecting unit and a density of the center pixel selected by the center pixel selecting unit is larger than a predetermined threshold value; a peak pixel detecting unit detecting peak pixels of the matrix, each peak pixel being the center pixel detected as having the maximum or minimum density by the maximum/minimum density detecting unit, and the absolute value of the difference with respect to the center pixel is determined as being larger than the threshold value by the determination unit; and a dot region detecting unit detecting one of the neighboring pixels including the peak pixels as being a dot region based on a relationship between the number of the peak pixels in a two-dimensional target region and the number of the peak pixels in each of two-dimensional neighboring regions of the target region.
According to the image processing apparatus of the present invention, the computation of peak pixels is performed not from the data of pixels at predetermined positions of the matrix but from the data of pixels chosen from the pixels at the positions symmetrical about the center pixel. The segmentation of a small character and a dot will become easy to perform. It is possible for the present invention to prevent the incorrect determination of a small character as being a dot It is possible for the present invention to easily detect a low-linear-density dot region with good accuracy.
Moreover, according to the image processing apparatus of the present invention, the segmentation of a dot region and a low-linear-density dot region can be easily and correctly performed, and improvement in picture quality is attached by, switching one of a first image processing and a second image processing to the other for each region based on the result of the segmentation.
Furthermore, according to the image forming apparatus of the present invention, the segmentation of a small character and a dot in the image data can be performed by using the image processing apparatus that easily and correctly segments image data into a small character and a dot, and the image forming apparatus can output the processed image with good picture quality.